1. Field of the Invention
The subject invention relates to a coil ignition dwell control system and to an associated fail-safe system in combination with a digital ignition advance computer.
2. Description of the Prior Art
Electronic ignition advance devices for internal combustion engines are becoming increasingly sophisticated and make use of very powerful computers. That is why the concept of controlling not only ignition advance but also the duration of current flow in the ignition coil can be applied without introducing significant complexity.
However, the devices that have been used up to now to perform this function present several drawbacks. In fact, handling the calculation of the moment of current initiation in the coil in the same manner as the moment of interruption (which, in fact, corresponds to the spark), i.e., computing this moment as a function of engine speed and of total conduction time required, makes it necessary to double certain functions in relation to the ignition advance computation itself, such as the measure of speed. The latter is generally performed at two levels, on the one hand for the calculation of the advance angle proper, and on the other hand for the conversion to engine angle of the time determined for coil control.
Furthermore, this calculation becomes more complicated as the relation between coil ignition dwell and speed diverges from a constant value. Indeed, it may be advantageous to lengthen the duration artificially for very low speeds in order to insure trouble-free starting of the engine.
Another drawback of systems now in use is that they do not provide a fail-safe device to insure advance to dead center in case of computer failure.